Setting up Active Directory for DR

When setting up a Disaster Recovery site its reasonably standard to deploy Active Directory in that site and let AD replicate as usual to ensure that you have a copy of the directory available.

However, replication between sites (using site links0 can only occur as often as once every 15 minutes, longer if you don’t change the defaults. This means that, if the disaster occurs in that time period, any changes that you make may well be lost.

To overcome this you can set up change based notifications for the site link. This makes updates between sites work as though they are within the same AD site. that is, pretty much as soon as a change occurs, it will replicate across the link. of course, this will generate more traffic between links especially for larger sites but you tend to ind that a DR replication link is usually fairly fast and low latency to allow replication of the virtual machines and data.

To enable notification driven replication between active directory sites, access the site link properties page and update the “options” value.

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The options attribute uses a bitmap. Its possible values are:

Decimal Value Binary Value Explanation
1 1 USE_NOTIFY
2 10 TWOWAY_SYNC
4 100 DISABLE_COMPRESSION

If you want to enable notification without compression (as you are on a LAN like connection, for example, between firewalled segments of the LAN) you can enter the value 5 to enable notification without compression.

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